Exhaust gas recirculation

ABSTRACT

A system is provided for optimizing recirculation of exhaust gases in the exhaust system of an internal combustion engine. A flow control valve is inserted in a passage interconnecting an intake system and exhaust system of the engine. Means are provided for actuating the flow control valve in response to vacuum pressure upstream of a throttle valve to increase the flow rate of exhaust gases to be recirculated; and means are provided to actuate the flow control valve to decrease the flow rate of recirculated gases in response to vacuum pressure downstream of the throttle valve.

United States Patent 11 1 Tomita 1 1 EXHAUST GAS RECIRCULATION [75]Inventor: Tsutomu Tomita, Okazaki, Japan [73] Assignee: Toyota JidoshaKogyo Kabushiki Kaisha, Toyota, Japan [22] Filed: Aug. 20, 1974 [21]Appl. No; 499,090

[30] Foreign Application Priority Data Oct. 2, 1973 Japan 48-110194 [52]US. Cl 123/119 A [51] Int. Cl. F02m 25/06 [58] Field of Search 123/119 A[56] References Cited UNITED STATES PATENTS 3,507,260 4/1970 Walker123/119 A 3,730,156 5/1973 Sarto 123/119 A 3,739,747 6/1973 Caldwell123/119 A 3,756,210 9/1973 Kuehl 123/119 A 3,774,583 11/1973 King123/119 A 3,800,765 4/1974 Thompson 123/119 A 5] June 10, 1975 3,814,0706/1974 Wertheimer 123/119 A 3,818,880 6/1974 Dawson et a1. 123/119 A3,834,366 9/1974 Kingsbury 123/119 A Primary Examiner-Wendell E. BurnsAssistant Examiner-David Reynolds Attorney. Agent, or Firm-Stevens,Davis, Miller & Mosher [57] ABSTRACT A system is provided for optimizingrecirculation of exhaust gases in the exhaust system of an internalcombustion engine. A flow control valve is inserted in a passageinterconnecting an intake system and exhaust system of the engine. Meansare provided for actuating the flow control valve in response to vacuumpressure upstream of a throttle valve to increase the flow rate ofexhaust gases to be recirculated; and means are provided to actuate theflow control valve to decrease the flow rate of recirculated gases inresponse to vacuum pressure downstream of the throttle valve.

3 Claims, 12 Drawing Figures PATENTEDJUN 10 ms SHEEY FIG.

FIG. 2

PATENTEnJuu 10 ms 3. 888.222 SHEET 2 FIG. 5

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PRESSURE UPSTREAM OF THROTTLE VALVE PATENTEI] JUN 1 0 i975 SHEET CONT-ROLLER I FIG. 7

ZJI' -5 SEE/ 5 5% Lo mzwuimma FIG. 8A

PRESSURE UPSTREAM OF THROTTLE VALVE PRESSURE DOWNSTREAM OF THROTTLEVALVE HEAVY LOAD FIG. 83

FIG. 8C

PRESSURE UPSTREAM OF THROTTLE VALVE EXHAUST GAS RECIRCULATION BACKGROUNDOF THE INVENTION The present invention relates to means for handling theexhaust gas of an internal combustion engine, and more particularly tomeans for recirculating a part of the exhaust gases discharged from theengine to an intake system thereof.

Exhaust recirculation systems have been used in internal combustionengine for the purpose of reducing maximum combustion temperature inorder to minimize the production of nitrogen oxides, which are a primarypollutioncausing exhaust component. In one prior art recirculationsystem, a part of the exhaust gases is injected upstream of a throttlevalve in an engine carburetor through a flow control valve. Since theexhaust gases must flow through the carburetor, the gases may cause suchproblems as corrosion of the carburetor, deposits on the throttle valvewhich cause sticking. and introduction of moisture in the throttle valvethat may produce freezing. It is therefore desirable to provide arecirculation system in which these problems are avoided.

In another prior art system, recirculated gases are injected downstreamof the carburetor throttle valve, into the intake system. In thissystem, the exhaust gases are recirculated due to the difference invacuum pressure in the intake manifold and the pressure of exhaustgases. Therefore, a large volume of the exhaust gases (large withrespect to the volume of intake air) is forced to be recirculated evenwhen the amount of intake air is reduced and it would be desirable toreduce the volume of recirculated exhaust gases. For example, the volumeof intake air to an engine is less than under a light load, but vacuumpressure in the intake manifold is increased so that an excessive amountof exhaust gas is recirculated. This causes such malfunctions asbreathing, surging, misfiring and other such problems.

SUMMARY OF THE INVENTION It is therefore an object of the presentinvention to provide an exhaust gas recirculation system for an internalcombustion engine which provides optimal volumes of recirculated exhaustgases and which is responsive to the volume of intake air, wherebyexhaust gas recirculation is responsive to engine operating conditions.

Briefly stated, there is provided in accordance with the presentinvention, means for controlling recirculation of exhaust gasesresponsive to engine operating conditions. A flow control valve ispositioned in an exhaust gas passage which interconnects an intakesystem and an exhaust system in the internal combustion engine. A firstdiaphragm in the flow control valve is actuated in response to vacuumpressure in the vicinity of the throttle valve, and a second diaphragmis actuated in response to vacuum pressure downstream of the carburetorthrottle valve in the intake system.

BRIEF DESCRIPTION OF THE DRAWINGS The means by which the foregoingobjects and features of novelty are achieved are pointed out withparticularity in the claims forming the concluding portion of thespecification. The invention, both as to its organization and manner ofoperation may be further understood by reference to the followingdescription taken in connection with the following drawings.

Of the drawings:

FIG. 1 is a diagram of a preferred embodiment of an exhaust gasrecirculation system constructed in accordance with the presentinvention,

FIG. 2 is a cross-sectional view ofa flow control valve for inclusion inthe system of FIG. 1;

FIG. 3 is a cross-sectional view of another form of flow control valvewhich may be used in the present invention;

FIGS. 4A and 4B are respective plots of flow control valve first andsecond diaphragm displacements versus pressure upstream and downstreamof the throttle valve respectively, and FIG. 4C is a family of curvesillustrating displacement ofa valve member in the recirculation passageunder various driving conditions;

FIGS. 5 and 6 are partial sectional views illustrating alternative formsof ports providing a vacuum pressure responsive to the degree of openingof a throttle valve;

FIG. 7 is a diagrammatic representation of another embodiment of asystem constructed in accordance with the present invention; and

FIGS. 8A, 8B and 8C are plots similar to those of FIGS. 4A, 4B and 4Cwhich are useful in understanding the operation of the embodiment ofFIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, thereis illustrated a system constructed in accordance with the presentinvention including an internal combustion engine 1 having an intakemanifold 2 connected thereto. An air source in the form of an aircleaner 3 provides air to the intake manifold 2. A venturi throat 4 isprovided between the air source 3 and the intake manifold 2. Fuel isprovided through a throttle valve 5 positioned between the air source 3and intake manifold 2. The throttle valve 5 is well-known, and in thepresent embodiment comprises a pivoted disc. The engine 1 is alsoprovided with an exhaust manifold 6, and an exhaust gas recirculationpassage 7 is connected between the intake manifold 2 and exhaustmanifold 6. A flow control valve 8 is provided in the recirculationpassage 7 for controlling the volume of exhaust gas recirculated back tothe intake manifold 2.

Referring to both FIGS. 1 and 2. the flow control valve 8 is describedin further detail. A housing 9 includes an intake port 10 communicatingwith the exhaust manifold 6. A valve member II is provided for flowcontrol in a valve chamber 12 which is a portion of the recirculationpassage 7 and which communicates with a discharge port 13. The dischargeport l3 communicates with the intake manifold 2. The valve member 11 isengageable with a valve seat 14 provided in the intake port I0 and ismovable by a valve stem 15. The valve stem I5 extends through thehousing 9 through an air-tight bushing 16 fitted at one surface of thevalve chamber II opposite the valve seat 14. The end of the valve stemIS opposite the valve member II extends into a diaphragm box I7 mountedon the hous ing 9. The diaphragm box 17 is divided by a first diaphragm18 into upper and lower diaphragm chambers 19 and 20. A coiled spring 21is disposed in the upper diaphragm chamber (upper meaning remote fromthe housing 9) 20 and normally biases the first diagraphm 18 toward thehousing 9. A second inner diaphragm box 22 is attached to the firstdiaphragm 18 within the lower chamber I9. The inner diaphragm box 22 isdi' vided by a second diaphragm 23 into an inner, lower diaphragmchamber 24 and an inner, upper diaphragm chamber 25. A coiled spring 26disposed in the inner, lower diaphragm chamber 24 normally biases thesecond diaphragm 23 upwardly.

The valve stem extends through both the first and second (outer andinner) diaphragm boxes 17 and 22 and has its upper end secured to thesecond diaphragm 23, so that movements of both the first and seconddiaphragms 18 and 23 may be transmitted by the valve stem 15 to move thevalve member 11. A bellows 27 is disposed concentrically with the valvestem 15 such that the lower diaphragm chambers 19 and 24 do notcommunicate with each other.

The upper chamber communicates via a port 28 to a three-port solenoidcontrol valve 29 (FIG. 1). A pipe line 30 extends from the valve 29 to aport 31 at a position adjacent the throttle valve 5 and upstreamthereof. The port 31 is located such that vacuum pressure at the port 31is proportional to the degree of opening of the throttle valve 5. Thethree-port solenoid control valve 29 is actuated by a controller 32 sothat the port 28 may be selectively coupled to the pipe line 30 or to aport 33 of the valve 29 communicating with the atmosphere. A temperaturesensor 34 responsive to ambient temperature and a sensor 35 responsiveto engine cooling water are each connected to the controller 32. Asensor 36 responsive to vehicle speed is also connected to thecontroller 32.

A port 37 is provided in the lower diaphragm chamber 19 communicatingwith surrounding atmosphere. An orifice 39 (FIG. 2) is disposed in aport 38 of the second, inner diaphragm box 22, and the port 38communicates via a flexible pipe 40 with a pipe line 41 extendingbetween the first, outer diaphragm box 19 and a port 42. The port 42communicates with the intake manifold 2 of the engine 1 downstream ofthe throttle valve 5. The orifice 39 is positioned to absorb variationsin vacuum pressure in the intake manifold 2 which are transmitted to theinner, lower diaphragm chamber 24. Therefore, sudden movement of thevalve member 11 in response to sudden variation in vacuum pressure inthe intake manifold 2 may be prevented, whereby smooth flow control isensured. A passage 43 is formed through the second, inner diaphragm box22 and the first diaphragm 18 and communicates with a flexible pipe 44which acts as a vent to the surrounding atmosphere to permit freemovement of the first diaphragm 18. Therefore, the pressure in theinner, upper diaphragm chamber 25 is equal to atmospheric pressure.

Referring now to FIG. 3, in which the same reference numerals denoteelements corresponding to those in FIG. 2, there is illustrated anotherform of flow control valve which may be used in the system of FIG. 1. Inthe flow control valve of FIG. 3, a passage 45 is formed in the valvestem 15 in an axial direction and communicates with the surroundingatmosphere through a passage 46 formed in the sealing bushing 16 andvalve casing 9. The pipe 44 and passage 43 of the embodiment of FIGv 2are thus replaced.

OPERATION In operation, the flow control valve 8 controls recirculationof exhaust gases from the exhaust manifold 6 through the recirculationpassage 7 to the intake manifold 2. When the throttle valve 5 is openslightly so that an upper end thereof is positioned adjacent the port31, the vacuum pressure admitted through the port 31 is in proportion tothe degree of opening of the throttle valve 5. However, when the upperend of the throttle valve 5 is opened widely, the throttle valve 5 doesnot significantly affect the pressure at the port 31, and the vacuumpressure admitted through the port 31 is almost equal to the vacuumpressure in the intake manifold 2.

The controller 32 operates in the following manner. The three-portsolenoid valve 29 is actuated in response to the output signal of thecontroller 32 so that the pipe line 28 extending from the flow controlvalve 8 communicates with the pipe line 30 when atmospheric temperature,temperature of cooling water, and vehicle speed, respectively, arewithin predetermined ranges. Vacuum pressure is admitted through theport 31, pipe line 30, the three-port valve 29, and the port 28 into theupper diaphragm chamber 20 of the flow control valve so that the firstdiaphragm 18 is caused to be moved upwardly against the biasing spring21. Since the first diaphragm 18 is fixed to the second, inner diaphragmbox 22, the valve 11 is moved upwardly a distance X1. As a result, thesectional area of the passage of exhaust gases defined by the valve seat14 and valve member 11 is increased, and the exhaust gases arerecirculated.

This description is now related to engine operation. When the engineload is light, the opening of the throttle valve 5 is small, and thevacuum pressure admitted through the port 31 is relatively high, so thatthe flow control valve 8 tends to increase the flow recirculation rateeven when the air intake into the engine 1 is rela tively (with respectto other engine operating conditions) low. However, the vacuum pressurein the intake manifold 2 is transmitted to the diaphragm chamber 24through the port 42, pipe line 41, the flexible pipe 40 and the orifice39, so that the second diaphragm 23 is caused to be moved downwardly.Consequently, the valve member 11 decreases the cross-sectional area ofthe passage for exhaust gases so that the flow of the ex haust gases tobe recirculated is further controlled.

However, when engine load is heavy, the opening of the throttle valve 5is large, so that vacuum pressure in the intake manifold 2 is decreased.Consequently, the downward displacement of the diaphragm 23 isdecreased, whereby the valve member 11 serves to in' crease thecross-sectional area of the exhaust gas passage, whereby the rate offlow of exhaust gases through the recirculation passage 7 is increased.

The above operation is further understood with respect to FIGS. 4A, 4Band 4C. The displacement of the first diaphragm 18 is denoted X1; andthe displacement of the second diaphragm 23 is denoted X2. X1 and X2 areof opposite signs. The displacement of the valve member 11 from thevalve seat 14 is denoted X3. X3 equals X1 plus X2. FIG. 4A is a plot ofX1 versus vacuum pressure at the port 31, and FIG. 4B is a plot of X2versus vacuum pressure at the port 42. FIG. 4C is a plot of a family ofcurves illustrating in which the ordinate is X3 and the abscissa istime, each curve being plotted for a different level of engine load. Forexample, the lowest value of X3 is obtained for light engine load, andhigher values are obtained for heavier levels of engine load.

When the ambient temperature, cooling water temperature of the engineand/or vehicle speed are higher or lower than a preset range, thethree-port solenoid valve 29 is actuated by the controller 32 so thatthe port 28 communicates with the surrounding atmosphere via the port33, and atmospheric pressure is introduced into the upper diaphragmchamber 20 of the flow control valve 8. As a result, the valve member 11is seated against the valve seat 14. Vacuum pressure is admitted throughthe port 42, pipe line 41, flexible pipe 40 and orifice 39 into theinner, lower diaphragm chamber 24 so that the valve stem movesdownwardly. Thus, the force pressing the valve member 11 against thevalve seat 14 is increased, strongly cutting off exhaust gasrecirculation. Therefore, strong cutoff force is provided even when thevacuum pressure in the intake manifold 2 is stronger than that in thevicinity of the throttle valve 5, which generally occurs in the case ofidling or deceleration.

The range of throttle valve 5 opening in which the vacuum pressureadmitted through the port 31 is proportional to the opening of thethrottle valve 5 in the embodiment of FIG. 1 is small. If it is desiredto increase this range, the cross-sectional area of the port 31 may beincreased as shown in FIG. 5. Alternatively, as illustrated in FIG. 6,two vacuum pressure admission ports 31 may be provided.

Referring now to FIGS. 7 and 8, in which the same reference numeralsdenote components corresponding to components in the embodiment of FIG.I, a similar embodiment is disclosed. FIGS. 8A, 8B and 8C are plotscorresponding to those of FIGS. 4A, 4B and 4C respectively, butindicating data for the embodiment of FIG. 7. In the embodiment of FIG.7 a vacuum pressure admission port 31 is opened at the venturi throat 4rather than in the vicinity of the throttle valve 5. In this embodiment,the vacuum pressure created in the venturi throat 4 is admitted to theport 31, the pipe line 30, the three-port valve 29 and the port 28 intothe diaphragm chamber of the flow control valve 8 so that the firstdiaphragm I8 is caused to move over a distance X], as illustrated inFIG. 8A. Since the vacuum pressure in the venturi throat is high whenthe volume of air passing therethrough is large, and low when the volumeis low, the flow rate of exhaust gases is controlled in proportion tothe volume of intake air. This provides for optimal exhaust gasrecirculation.

The vacuum pressure in the intake manifold 2 is transmitted to theinner, lower diaphragm chamber 24 so that the second diaphragm 23 iscaused to be moved in the direction opposite that of the movement of thefirst diaphragm 18 over the distance X2. as illustrated in FIG. 8B. Theresulting displacement X3 of the valve member I] of the flow controlvalve 8 is such that the flow rate of the exhaust gases to berecirculated is controlled in response to the volume of intake air intothe engine I or in response to engine load. Furthermore, when the engineload is light, the flow rate of exhaust gases to be recirculated may becontrolled in response to the vacuum pressure in the intake manifold 2.

In the embodiment of FIG. I, the vacuum pressure under full load in thevicinity of the throttle valve 5 admitted through the port 31 is lowerthan a predetermined value (FIG. 4A) so that the displacement XI of thefirst diaphragm I8 is zero. Thus. the valve member II is forced againstthe valve seat I4, thereby cutting off the recirculation of the exhaustgases. In the embodiment of FIG. 7, however. even under full load. asmall vacuum pressure is admitted from the venturi throat 4 through aport 31 so that the first diaphragm I8 is caused to be moved over ashort distance X1 (FIG. 8A). Consequently, the complete cutoff by thevalve member 11 and the valve seat I4 becomes difficult. In order toovercome this problem in the present invention, a switch 47 is providedconnected to detect the opening of the throttle valve 5. The switch 47is connected to operate so that when the throttle valve 5 is wide open,a signal is connected to the controller 32 to actuate the three-portvalve 29 such that the pipe line 28 communicates with atmosphericpressure at the port 33. The valve member 11 is positively seated inthis manner as described above.

As hereinabove described. the flow control valve 8 may control the flowrate of the exhaust gases to be recirculated in response to vacuumpressure in the vicinity of the throttle valve 5 or in the venturithroat 4. Under a light load in which the volume of intake air is less,the flow control valve controls the flow rate of exhaust gases to berecirculated in response to vacuum pressure in the intake manifold,thereby preventing the excessive recirculation of exhaust gases.Therefore, optimal exhaust gas recirculation control may be ensured inresponse to engine operating conditions. Therefore, malfunctions such asbreathing, surging, and misfiring are substantially eliminated, enginedfficiency may be remarkably increased, while at the same time reducingproduction of pollutants. The specification has been written with a viewtoward enabling those skilled in the art to make modifications in thespecific embodiments shown above to provide an exhaust gas recirculationcontrol system constructed in accordance with the present invention.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

l. A system for controlling recirculation of exhaust gases from anexhaust manifold to an intake manifold in an internal combustion engine,a throttle valve of the engine being provided upstream of the intakemanifold, comprising, in combination:

a recirculation passage connected between the exhaust manifold and theintake manifold;

a valve disposed in said recirculation passage including a valve memberdisposed such that the volume ofgases flowing in said recirculationpassage is proportional to the displacement of said valve memher;

a first diaphragm box, said first diaphragm box being divided by a firstdiaphragm into a first diaphragm chamber and a second diaphragm chamber,means communicating said first diaphragm chamber with the surroundingatmosphere and means communicating said second diaphragm chamber withsaid intake manifold upstream of the throttle valve;

a second diaphragm box attached to said first diaphragm, said seconddiaphragm box being divided by a second diaphragm into a third diaphragmchamber in communication with the surrounding atmosphere and a fourthdiaphragm chamber in communication with the intake manifold downstreamof the throttle valve, displacement of said first diaphragm in a firstdirection being caused by vacuum pressure admitted in said secondchamber, and displacment of said second diaphragm in an oppositedirection being caused by vacuum pressure admitted into said fourthdiaphragm chamber; and

means connecting said second diaphragm to said 2. A system according toclaim 1 wherein means are valve member such that the degree of openingof provided communicating said second diaphragm chamsaid recirculationpassage due to displacement of ber with said intake manifold in thevicinity of the said valve member increases with displacement ofthrottle valve. said first diaphragm and decrease with displace- 3. Asystem according to claim 1 wherein means are merit of said seconddiaphragm, whereby recirculaprovided communicating said second diaphragmchamtion of exhaust gases varies in response to engine her with aventuri throat upstream of the throttle valve. operating conditions.

1. A system for controlling recirculation of exhaust gases from anexhaust manifold to an intake manifold in an internal combustion engine,a throttle valve of the engine being provided upstream of the intakemanifold, comprising, in combination: a recirculation passage connectedbetween the exhaust manifold and the intake manifold; a valve disposedin said recirculation passage including a valve member disposed suchthat the volume of gases flowing in said recirculation passage isproportional to the displacement of said valve member; a first diaphragmbox, said first diaphragm box being divided by a first diaphragm into afirst diaphragm chamber and a second diaphragm chamber, meanscommunicating said first diaphragm chamber with the surroundingatmosphere and means communicating said second diaphragm chamber withsaid intake manifold upstream of the throttle valve; a second diaphragmbox attached to said first diaphragm, said second diaphragm box beingdivided by a second diaphragm into a third diaphragm chamber incommunication with the surrounding atmosphere and a fourth diaphragmchamber in communication with the intake manifold downstream of thethrottle valve, displacement of said first diaphragm in a firstdirection being caused by vacuum pressure admitted in said secondchamber, and displacment of said second diaphragm in an oppositedirection being caused by vacuum pressure admitted into said fourthdiaphragm chamber; and means connecting said second diaphragm to saidvalve member such that the degree of opening of said recirculationpassage due to displacement of said valve member increases withdisplacement of said first diaphragm and decrease with displacement ofsaid second diaphragm, whereby recirculation of exhaust gases varies inresponse to engine operating conditions.
 2. A system according to claim1 wherein means are provided communicating said second diaphragm chamberwith said intake manifold in the vicinity of the throttle valve.
 3. Asystem according to claim 1 wherein means are provided communicatingsaid second diaphragm chamber with a venturi throat upstream of thethrottle valve.